1. Field of the Invention
This invention relates to multiple countershaft, constant mesh, mechanical transmissions, primarily for use in trucks, of the type described in U.S. Pat. No. 4,640,145, the disclosure of which is incorporated herein by reference. The invention features improved input shaft and input drive gear backlash structure for such transmissions which minimizes the occurrence of rattle or noise produced when the vehicle is immobile, the transmission is in neutral, the master clutch is engaged and the engine is operating at idle speed. The inventive structure is applicable to the interconnecting means of the vehicle engine and transmission.
2. Description of the Related Art
Multiple countershaft transmissions of the type described in U.S. Pat. No. 4,640,145 have proven to be highly acceptable in trucks and other heavy-duty applications. However, when a driver stops a truck to eat, sleep or for other reasons and leaves the engine running at idle speed, a constant undesirable noise is emitted from the transmission. The rattle or noise is initiated by the engine idling or turning at a non-uniform velocity. The engine speed will increase when a piston fires, followed by a slowing until the next firing of a piston. This alternative increase and decrease of engine output speed, known as surging, causes a nonuniform input to the transmission. However, due to inertia the transmission input gearing tends to function uniformly. Thus, the input drive means and the input gear of the transmission tend to be nonsynchronous, the result of which is a rattle which can be very disturbing.